An electronic device having chassis or a touch screen touched by a user when used, such as a tablet terminal, a smartphone, a mobile phone, or a computer, may be equipped with an actuator (haptic actuator) to give haptic feedback to a human body. The haptic actuator transmits vibration to a vibrating body such as the touch screen or the chassis according to an event generated by a system. The user perceives vibration in a human body region in contact with the vibrating body or perceives the vibration as sound. The haptic actuator uses electric power as a drive source and can be divided roughly into an impact type and a vibration type depending on the nature of vibration.
Representative examples of the impact type can include a Shape Memory metal Impact Actuator (SIA) using shape-memory alloy and a piezoelectric actuator using a piezoelectric element. The impact type uses a vibration element to hit a chassis or a keyboard plate so as to apply transient vibration. Representative examples of the vibration type can include an ERM (Eccentric Rotating Mass) actuator using an eccentric motor, a linear resonant actuator (LRA) which causes an alternating current to flow through a coil in a magnetic field so as to vibrate a mover, and the like. The vibration type applies vibration with a constant amplitude for a time necessary for the vibrating body to vibrate.
A vibration actuator, for example, may includes a mover linearly vibrates in a surface direction in cooperation with a coil and a magnet by the application of a rectangular-wave or sine-wave current to the coil fixed to a chassis. A PWM-controlled drive signal is supplied to a haptic actuator using a piezoelectric element, a voice coil, or a solenoid to adjust the intensity of vibration.
In general, the LRA is so used that an alternating pulse voltage with a frequency close to a resonant frequency will be applied to a mover to vibrate in a steady state. It is also considered that the LRA is used as an impact type using a transient vibration region immediately after pulse voltage is applied. When five to six pulse voltages with a large amplitude are applied to the LRA, large vibration occurs in a short time to enable a user to feel the impact. Since the bodily sensation of haptic feedback is different from individual to individual, it is desired that the magnitude of impact can be adjusted for each user. One method of changing the magnitude of impact is to change the amplitude of each pulse voltage, but a circuit for performing the continuously changing of the amplitude can be very large in scale.
Consequently, it would be preferable to provide an improved haptic feedback system to apply impact to an electronic device.